Concrete is a manufactured mixture of cement and water, with aggregates of sand and stones, which hardens rapidly by chemical combination to a stonelike, water-and-fire-resisting solid of great compressive but low tensile strength.
Because it can be poured into forms while liquid to produce a great variety of structural elements, it provides an economical substitute for traditional materials, and it has the advantages of continuity (absence of joints) and of fusing with other materials. Reinforced concrete was developed to add the tensile strength of steel to the compressive strength of mass concrete. The steel reinforcement is employed to take full advantage of the plastic, or sculptural, character of concrete. It can be joined or bent to unify supporting members with the floors and the coverings they carry.
Three 20th century developments in production are destined to have a radical effect on architecture. The first, concrete-shell construction permits the erection of vast vaults and domes with a concrete and steel content so reduced that the thickness is comparatively less than that of an eggshell. The second development, precast-concrete construction, employs bricks, slabs, and supports made under optimal factory conditions to increase waterproofing and solidity, to decrease time and cost in erection, and to reduce expansion and contractions. Finally, prestressed concrete provides bearing members into which reinforcement is set under tension to produce a live force to resist a particular load. Since the member acts like a spring, it can carry a greater load than an unstressed member of the same size.

Concrete Sheel
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Prestressed concrete external image StressedRibbonBridgeUnderside7138.JPG


Precast concrete
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Reforce concrete

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Tilt-up panel construction, tiltwall construction, precast concrete building construction are terms used for cement building processes. Tilt-up and tiltwall are two terms used to describe the same process. For a tilt-up concrete building, the walls are created by assembling forms and pouring large slabs of concrete called panels directly at the job site. Tiltwall panels can sometimes be extremely wide and/or tall. Tilt-up panel have been measured at just over 69 feet across and almost 93 feet from top to bottom.

The precast concrete building process is similar to tilt-up construction, work crews don't set up forms at the job site to create the panels. Instead, workers pre cast concrete panels at a large manufacturing facility. Because the precast concrete forms are poured indoors, this activity can take place regardless the weather conditions.